(1) Field of the Invention
The invention relates to a device for the continuous determining of the hardness of a smokable article from the mechanical properties of a rod of tobacco fibres in the manufacture of such a smokable article with a former finger for compacting the rod of tobacco fibres to a given diameter.
2. Description of the Prior Art
In cigarette production, more and more attention is being devoted to the hardness of the cigarettes at the quality control stage, since it is possible to determine in a relatively simple manner from measuring the hardness whether a smokable article, for example a cigarette, is adequately filled or not. And it is precisely the inadequate filling of smokable articles which is a frequent ground for complaints.
Therefore, in an article from "Contributions to tobacco research", Vol. 4, Number 7, December, 1968, a device for testing the hardness of cigarettes is described with which the changes in diameter of cigarettes under specific loads is measured over a given time and the hardness is ascertained therefrom. But this substantially static process is suitable only for selected sample tests, in other words cannot be used for current continuous monitoring of the hardness of the smokable articles during manufacture and for appropriate regulation of the whole production operation.
U.S. Pat. No. 3,411,513 also shows a method wherein a moved, finished, tobacco rod wrapped in paper is deformed by a stream of air, and the associated follow-up of the nozzle is ascertained. The nozzle movement which occurs has a correlation with the filling ability of the tobacco and thus the hardness of the cigarette. But the information obtained in this way is influenced by diameter fluctuations and the porosity of the cigarette paper, so that only in a few cases is there a precise correlation with the static measurement of hardness via the determining of depth of penetration as is known from the cited article.
Methods are also known wherein the deformation of the format or former finger under the influence of the stream of tobacco fibres flowing past is ascertained and a continuous measurement signal is thus obtained which is to be correlated to the hardness of the finished cigarette. For example German OS No. 2 241 774 shows a device wherein a force pickup, generally a strain gauge, is provided which ascertains the deformation of the supporting bridge for the former finger. Another variant is known from German OS No. 2 457 141, wherein the deflection of the front portion of the divided former finger under the action of the rod of tobacco fibres is ascertained. And finally U.S. Pat. No. 2,667,172 shows a device which at various places ascertains the vertical and horizontal forces which the rod of tobacco exerts on its guide and more particularly on the former finger. For example the width of the gap between the front end of the former finger and a pickup i.e. the deflection of the front end of the former finger, is ascertained.
In the case of all these known measuring methods, however, the correlation between the deformation of the former finger and the hardness of the finished cigarette is relatively slight i.e. the measurement result correlates linearly with the hardness of the finished cigarette only in situations where the pickup ascertains the deformation of the former finger at a place where the diameter of the skein of tobacco fibres corresponds approximately to the tobacco diameter of the finished smokable article, as is known from the older application No. P 33 06 543.8-23.